1. Field of the Invention
This invention relates to gasification of carbonaceous materials, and more particularly to apparatus for cooling the particles separated from product gas of fluidized bed gasification reactors.
2. Description of the Prior Art:
In reactors for the gasification of carbonaceous materials, such as coal, a combustible product gas is produced, as well as solid waste products such as agglomerated ash. In the Process Development Unit (PDU) fluidized bed gasification reactor being operated for the United States Government, particulate coal is injected through one of a number of concentric tubes extending upwardly into the center of a vertical bed-containing pressure vessel. Fluidization occurs in the upper sections.
In the PDU fluidized bed gasification reactor, the product gas from gasified coal contains a significant amount of particles whose temperature is near the gasifier exit temperature of approximately 1800.degree. F. These particles must be removed from the product gas and disposed of to prevent disruption of downstream processing of the product gas. During separation by, for example, a cyclone separator, the particles fall by gravity to the bottom of the separator, then through piping to a particulate discharge system. This discharge system has as its purpose the retention of product gas during the discharge of particulate from the gasification system. As a result, numerous parts of the discharge system are made of rubber, plastic or other compositions which will not stand up to prolonged periods of high temperature. It is therefore necessary to cool the hot particulate prior to its entry into the discharge system.
At the same time, the characteristics of the hot particulate require an improved heat exchanger. Since the particle/wall contact in a straight tube heat exchanger is intermittent and of short duration, what is needed is a heat exchanger which will improve the heat exchange rate. In addition, since a particle stream is involved, an efficient means is needed for moving the particles through the heat exchanger which will not be adversely effected by the heat of the particles.